This invention relates to a method of and an apparatus for measuring and adjusting the length of a weft thread continuously delivered from a stable weft thread idler shaft. The invention is particularly suitable for shuttleless weaving looms wherein a prior exactly measured length of a weft thread is introduced into the shed as it is, as for instance in the case of jet looms.
Known methods for measuring the length of the weft thread can be substantially divided into two categories: (1) a measuring with discontinuous delivery of the weft thread, and (2) a measuring with a continuous delivery of the weft thread supplied from a stable weft thread idler shaft.
(1) Measuring with a discontinuous delivery of the weft thread is substantially performed by supplying the weft thread from a stable idler shaft, seizing it at a given moment by a rotating lug in order to wind it with the required length on a measuring drum, subsequently removing it by the picking mechanism of the loom, and introducing it into the shed. The weft thread remains thereafter at rest up to its next seizing by the lug. An advantage of this method is that the length of the weft thread can be adjusted within a substantially large range by changing the moment of seizing and thus the length of the weft thread wound on to the measuring drum can also be changed. A drawback, however, is that in case of an intermittent removal the weft thread is subject to substantial stress due to inertia caused by its repeated stopping and being seized in the course of measuring. The time required for measuring is thus limited; this also influences any further increase of the speed and also the efficiency of production of the loom.
(2) In case of the other method, that of measuring the weft thread with continuous delivery, the weft thread, during the course of the whole operating cycle of the weaving loom is taken off uniformly and at a practically constant speed from a stable weft thread idler shaft. This apparatus, for measuring a continuously delivered weft thread, is substantially composed of a measuring drum, the circumference of which corresponds to the required length of the weft thread. The weft thread, in order to secure a correct removal, is pressed against the circumference of the measuring drum by a pressure roller. At a given moment, the prior measured length of the weft thread is removed by the picking device and is introduced into the shed.
There are also measuring devices with continuous delivery of the weft thread having a measuring drum of reduced size upon which a number of turns of the weft thread are wound.
The weft thread is less stressed in measuring devices with a continuous delivery and they are therefore also more advantageous for high speed weaving looms. Their drawback, however, is that if changes of the length of the weft thread are required, a measuring drum with a variable diameter or a set of exchangeable measuring drums has to be used. However; this is costly and wearisome to operate.